Film or sheet forming apparatus



y 15, 1941- H. E. VAN DERHOE F 2,249,507

7 FILM QR SHEET- FORMING APPARATUS Filed March 6, 1940 NVENTOR BY y I AT'ToRNE S fiS/YRYE. l/4NZRERH0EF Patented July 15, 1941 UNITED ST FILM OR SHEET FORTVHNG APPARATUS Application March s, 1940, Serial No. 322,579

10 Claims.

This invention relates to the art of making film base or sheeting by coating solutions of cellulosic material onto a smooth moving surface such as a belt or wheel, and more particularly to an improved type of apparatus for feeding the solution to the moving surface in such a way that a smooth even sheet throughout results.

As is well known in the art, cellulosic film or sheeting 'is formed by spreading a thin coating of a desired material, generally a solution of a cellulose ester such as .cellulose nitrate, or cellulose acetate in suitable solvents, onto an appropriate surface and permitting, or causing, the solvents to evaporate therefrom. The device usually employed for feeding the solution onto the wheel comprises a v-shaped hopper provided with blades mounted at an angle to one another at the apex of the V, and at least one of which is adjustable with respect to the other so as to provide a means of controlling the thickness of the dope stream and, therefore, the sheet being formed. Such a device is shown in conventional form in U. S. Patent 1,900,873, issued on March 17, 1933, to me.

It has been found that serious dificulties often arise from the tendency of the cellulose ester solution to form slugs, or encrustations, on the edges of each or both blades, and'since, when these slugs form, they project down into the dope stream and give rise to uneven coating and the L formation of streaks the finished product which render it unfit for use. 'These difficulties are more serious in the manufacture of the thinher-types of sheeting and film supports than in the thicker materials, and they even result in the production of'holesor voids in the products.

It has beenfound that this slugging action is due to the fact that small amounts of thecellulose ester solution creep along theouter surfaces of the blades as it flows out of the hopper instead of being carried along in the dope stream onto the wheel. The solvent evaporates from the small portions of dope" and causes them to solidify, thus forming slugs. These slugs tend t'oincrease in size dueto further 'acc'retions of "done that eventually become sufficiently large to project below the edges of the blades and cause the disastrous results" above referred to; Iam

' aware that difierent steps 'have'been takento overcome this slugging, 'suchfor instance as the maintaining of-a solvent vapor in the vicinityof the ends of the'hopper blades at such concentrations as will prevent the formation of accretions of solidified material at that point, but I have overcome this difficulty by replacing the customary stationary hopper blades by moving members which continually rotate into the supply of cellulosic solutions and are doctored clean of solution prior to becoming exposed to the air,

whereby a continually new line of contact for the dope leaving the hopper is presented.

Therefore, one object of the present invention is toI foVide a new type of coating hopper for in saying an uninterrupted and even coating of the cellulose ester solution in film and sheet making.

Another object is to provide such a hopper in which the edges of the discharge slot thereof are continually moving counter to the direction of flow of solution through said slot, whereby the solution actually contacting such edges is engaging said rollers is carried back into the.

hopper where it is redissolved in the event it tends to become solid. And yet another object is to doctored clean as they leave the solution so that the surface contacting'the flow of solution from.

the'hopper is always free of slugs or deposits of any kind.

And yet another object is to provide a hopper of the type described wherein a guide member is located between the rollers and extends from within the hopper toward the film forming ele-.

ment down the faces of which'the solution is adaptedto flow in a smootheven sheet.

And still another object is to provide means for optionally closing said discharge slot, and I which means may include ,a stopper movable. into and out of a position wherein it extends into said slot and'into engagement with the two rollers simultaneously.

.The novel features that I consider character.- istic'of my invention are set forth with particue larity in the appended claims; *The invention itself, howevenboth'as to its organization, and

its method of operation, together with additional objects and advantages thereof, will best be 'un derstood from the following description when read in connectionwith thegaccompanying drawing in which, I a

V Fig. 1 is a cross section ofa hopper constructed provide a hopper: 1 of the type described wherein the rollers are Referring to the drawing, the numeral lfl'diesignates, generally, a device for feeding the cellulosic solutions, or dope, which, for example, may be a solution of cellulose nitrate or acetate in a suitable solvent, such as acetone or other liquid,

to the surface of the wheel or drum II. This feeding device may hereinafter conveniently be referred to as a dope hopper, the cellulosic solution as dope, and the wheel or drum as coating wheel, since these terms are the terms customarily employed in the art. The hopper may be adjustably mounted, or suspended, over the wheel by a suitable means, not shown, in such manner that it may be lowered to, or'raised from, the coating surface as occasion may require.

The hopper H] as shown may comprise an elongated trough having hollow side walls l2 and end walls I3. The upper end of the hopper may be normally opened and may be closed by a removable cover l4 having flanges [5 along its opposite edges adapted to rest on a shoulder l6 formed in the upper end of the side walls [2, see Fig. 1. The hopper is adapted to contain a supply of coating dope S, and any suitable means, not shown, may be provided for introducing dope into said hopper in order to maintain a substantially constant level of dope therein. One of the end walls l3 may be provided with a transparent window 11 through which the dope level may b observed, and, if desired, a scale, not shown, may be placed on the face of said window to accurately indicate the level of the dope in the hopper. The side walls l2 of the hopper are made hollow, and are placed in communication in any suitable way, so that a heating medium, such as hot water or steam, may be circulated therethrough for the purpose of maintaining the dope in the hopper at any desired temperature.

The construction of that part of the hopper just described forms no part of the present invention and may be of the form described, or of any other well-known construction. The present invention relates to the construction of the discharge part of the hopper which will now be described. Referring to Fig. 1, the lower ends of the side walls I2 of the hopper converge toward one another to form an opening through which the dope may flow by gravity. The customary stationary blades usually found on a hopper of this type are replaced in the present instance by a pair of ground rollers 2| mounted in parallel spaced relation in, or below, the opening 2:: in the hopper, the space between said rollers forming the actual discharge slot of the hopper through which the dope is adapted to flow to the coating wheel ll.

Therollers 2i may be mounted in liquid tight connection with the lower ends proper of the hopper side walls l2 if desired so that no dope can flow between these respective parts. However, for the purpose of convenience and simplicity I have chosen to show the rolls 2| mounted in spaced relation to said side walls, and. the space: between the side walls and the rollers renderedi liquid tight by resilient doctored blades 23 ex-' tending from the ends of side walls to the periph-- cry of said rollers. These doctored blades 23 may be made of a spring steel, or any other suit-- able material not subject to attack by the dope,. and, as shown, each may be detachably mounted; at one end in overlapping relation with side walls; of the hopper by being mounted in a recess in. the inside face of the ends of each side wall. by a clamping plate 24 adapted to be bolted to: the side wall as shown, the bolts 25 of said clamp-- ing plate necessarily passing through holes in the ends of the doctored blades. The free ends of each of the doctored blades is adapted to be firmly pressed against the periphery of the roller 2| adjacent thereto and acts to wipe the roller clean of solution as will be hereinafter described. It will be appreciated that the doctored blades 23 extend the full length of the hopper l0, and that since they serve to direct the dope into the discharge slot between the rollers 21 they form a part of the hopper proper.

Referring now particularly to Fig. 3, it will be observed that the rollers 2| are each rotated in a direction counter to the direction of flow of'the dope through the discharge slot between the rollers. The advantage of rotating the rollers: 2| counter to the direction of flow of the dope is derived from the fact that any tendency that the film of dope actually contacting the rollers might have to flow around the rollers and out of the main dope stream where it might solidify and form slugs, as in the case of stationary hopper blades, is overcome. Further, due to the fact that the thin film of dope actually contacting the surface of the rollers 2| is continually carried back to the doctor blades 23 which wipe it off into the hopper, no given film of dope remains in contact with the rollers or atmosphere for any appreciable time to permit the formation of slugs or encrustations at any point. The peripheries of the rollers are wiped clean of dope prior to coming in contact with the atmosphere so that no slugs tend to form thereon, and a continually new line of contact for the dope leaving the hopper is presented.

The rollers 2| are to be rotated slowly and preferably at the same speed, and any suitable driving means for the rollers may be utilized. For the purpose of illustration, I have shown the shaft 28 of each roller, extending to the outside of the end wall of the hopper, provided with a spur gear 29, each of said gears being in mesh with a driving gear 30 adapted to be driven from any source of power. I have found that if the rollers 2| are rotated slowly, only the thin film of dope contacting the same tends to move in the direction of the rollers and the main stream of dope tends to flow out of the discharge slot between the rollers in a smooth even stream of uniform thickness and free of all imperfections which are incident to the formation of slugs, or accretions of solid dope on the stationary blades of known hoppers. It will be appreciated that the flow of dope between the rollers'2l for a given width of slot will depend upon the head, or pressure, behind the supply of dope. Consequently, in order to obtain a sheet of uniform thickness it is necessary to maintain the level of the dope ina gravity fed hopper substantially constant; or if a pressure is used behind the flow of dope, that such pressure be maintained substantially constant.

The discharge slot between the rollers 2| may be closed, when the hopper is not in use, by

a metal stopper 3| mounted vertically above the discharge slot to move into and out of the same, and such stopper may have concave ground sure. g. stainless steel or the like, hence the necessity of grinding the concave surfaces 32 to fit the rollers. However, if a more or less resilient material were available which would not be attacked by the dope, it will be appreciated that a stopper made of such material would not necessarilyhave to be so accurately formed,but could rely upon its resiliency to make the desired fluid tight closure with the rollers.

Inasmuch as the stopper is quite long, extending the full length of the discharge slot, it must be moved to and from the slot uniformly throughout its length, and elevating and lowering adjusting means therefor must be provided which will give a smooth and uniform adjustment of the stopper throughout its length. Such an adjusting means may comprise a plurality of vertical adjusting rods 35 extending. through, and rotatably mounted relative to, the cover I l. The number and spacing of these rods will necessarily be determined by the length of the stopper so as to insure a uniform movement of the same throughout its length. The lower end of each of the rods 35 is threaded and is in threaded engagement with an internally threaded shank 36 formed on the top of the stopper. Each rod 35 is rotated through a gearing including a worm gear 3'! fixed to the end of the rod and engaging a spiral gear 38 moiuited on a shaft 39 extending lengthwise of the cover M, said shaft 39 being rotated by a handcrank, or any other suitable means, not shown. The ends of the stopper (H are flush with the end walls [3 of the'hopper, see Fig. 2, so that the stopper, or the shank 36 thereon, cannot rotate. Therefore, when the rods 35 are rotated by the described gearing, the

stopper is moved to or'away from the discharge slot depending upon the direction of rotation of the shaft 39 by virtue of the threaded engagement between said rods and the shanks 36 on the stopper. To prevent a back lash in the threaded engagement between the rods 35 and the shank 36, the coil spring 36 encircling each quite contact the wheel H.

rod is held under compression between the top ofthe shank 36 and a collar 45 carried by the rod. A metal sleeve 42 may be slipped over the shank. 36 in covering relation to the coil spring and threads on the rod 35 to prevent the dope from coming in contact therewith.

I have found that an unusually even and uniform feed of dope can be discharged onto the coating wheel if a guide member 45 is suspended in the discharge slot between the rollers 2i and in the path of the stream of dope issuing through said slot. Such a guide member may constitute a sheet of stainless steel long enough to extend.

the full length of the discharge slot in the hopper, and may be suspended in proper relation in said discharge slot by being fixed in a groove d6 of the lower end'of the stopper. The opposite faces of the end of the guide member 45 extend ing below said stopper may be ground as shown in Fig. 3 so as tocome substantially to a point and curve in the direction of rotation of the coating wheel, so that the dope flowing down both facesof the same will converge into a single (ill sheet properly directed'onto the wheelprior to engaging the same, see Fig. 3. The end' of the guide member extending below the stopper 3| should preferably be of such length that when the stopper is moved to its slot closing position, see Fig. 1, the end of the guide member will not When the stopper is moved to open the discharge slot, see Fig. 3, the end of the guide member will be spaced approximately one-quarter of an inch from the coating wheel although the operation of the device is not limited to this particular spacing between theend of the guide member and wheel. Referring: to Fig. 3, it will be noticed that when the discharge slot is opened the guide member 45 is completely encased by two streams of dope running down both faces thereof and as a consequence of which there is no chance for any part of the dope to flow out of the main stream where the solvent can become separated therefrom to form slugs or encrustations which would tend to disrupt the uniformity of the sheet of dope.

Although I have described my invention with reference to the manufacture of, celluloseacetate or nitrate films or sheetings, it is equally applicable to the production of such products from any typeof cellulosic solution such as those of the higher single organic esters of cellulose including cellulose propionate, cellulose, acetate propionate, cellulose acetate butyrate, cellulose acetate stearalte, and others. Furthermore, while I have illustrated my invention as applied 'to a circular type of coating surface, namely a wheel surface, it will be apparent that the invention is equally adaptable, with slight modifications well known in the art, to a flat coating or film forming surface such as that of a metal belt passing continuously underneath the hopper in a horizontal direction as shown in U. S.

patent to Stevens et al., No. 573,928.

It will be apparent from the above description that I have provided a hopper having a dopedischarge means which overcomes the formation of slugs or encrustations of solidified material on or in the vicinity of the dope discharge slot, thereby precluding the possibility of streak formation, tearing or voids in the film sheeting during its manufacture, and eliminating one of which would provide a movable, edge for the or Y discharge slot and which edge could be contin- I ually moved in a direction counter to the flow of dope through the slot so as to continually pre sent a new and clean line of contact'tovthe' dope. Such a means might include an endless metal belt passing over spaced driving rollers, one of 7 said guiding rollers being located in the position assumed by the rollers in the disclosed arrangement so that the curved portion of the belt would j form one edge of the dope discharge'slot.

Although I have shown and described certain specific embodiments pf my invention, I am fully aware that many modificatio-ns'thereof are possible. My invention, therefore, is not to berestricted except in so far as is necessitated by, the prior art and by thespiri t of the appended claims.

Having thus described myinvention, what If claim is new and desire to secure by Letters Patent of the United States is: 1. In a film or sheet forming device the combination with a hopper having an opening through which a film forming solution is adapted to be fed to a moving film forming element located adjacent thereto, of means associated with said opening for directing said solution to the film forming element in the form of a sheet, said means including a pair of movable members each positioned in liquid tight contact with that portion of the hopper forming opposite sides of said opening, and spaced apart to form a slot through which the solution is adapted to flow, and means for moving each of said members in a direction counter to that of the flow of solution through said slot.

2. In a film or sheet forming device the combination with a hopper having an opening through which a film forming solution is adapted to be fed to a moving film forming element located adjacent thereto, of means associated with said opening for directing said solution to the film forming element in the form of a sheet, said means including a pair of rollers each positioned in liquid tight contact with that portion of the hopper forming opposite sides of said opening, and spaced apart to form a slot through which the solution is adapted to flow, and means for rotating each of said rollers in a direction counter to that of the flow of solution through said slot.

3. In a film or sheet forming device the combination with a hopper having an opening through which a film forming solution is adapted to be fed to a moving film forming element located adjacent thereto, of means associated with said opening for directing said solution to the film forming element in the form of a sheet, said means including a pair of movable members each positioned in liquid tight contact with that portion of the hopper forming opposite sides of said 7 opening, and spaced apart to form a slot through which the solution is adapted to flow, an elongated guide member located intermediate and spaced from said movable members and extending through said slot from within said hopper toward, but out of contact with, the film forming element for directing a sheet of said solution to the same, and means for moving each of said members in a direction counter to that of the flow of solution through said slot.

4. In a film or sheet forming device the combination with a hopper having an opening through which a film forming solution is adapted to be fed to a moving film forming element located adjacent thereto, a pair of movable members positioned below and adjacent said opening and spaced apart to provide a slot through which said solution is adapted to flow, means providing a liquid tight duct between the movable members and the hopper, a guide member located intermediate and spaced from said movable members and extending through said slot from within said hopper toward, but out of contact with, the film forming element for directing a sheet of said solution to the same, the end of said guide member adjacent the film forming element reduced in cross section whereby the opposite faces thereof substantially meet at a point and are curved in the direction of movement of said element, and means for moving each of said members in a direction counter to that of the flow of solution through said slot.

5. In a film or sheet device the combination with a hopper having an opening through which a film forming solution is adapted to be fed to a moving film forming element located adjacent thereto, of means associated with said opening for directing said solution to the film forming element in the form of a sheet, said means including a pair of rollers mounted below and adjacent said opening and spaced apart to provide a slot through which said solution is adapted to flow, a doctor blade connected to the hopper at each side of said opening and extending into surface contact with the roll adjacent thereto to form a liquid tight duct from the opening in the hopper to the slot between said rolls, a guide member located intermediate and spaced from each of said rolls and extending through said slot from within said hopper toward, but spaced from, the film forming element for directing a sheet of said solution to the same, and means for rotating said rolls in a direction counter to that of the fiow of solution through said slot.

6. In a film or sheet forming device the combination with a hopper having an opening through which a film forming solution is adapted to be fed to a moving film forming element located adjacent thereto, of means associated with said opening for directing said solution to the film forming element in the form of a sheet, said means including a pair of rollers mounted below and adjacent said opening and spaced apart to provide a slot therebetween in communication with the opening in the hopper through which the solution is adapted to flow, means between said hopper and rolls for rendering a liquid tight conduit between said opening and said slot, means for driving said rolls in a direction counter to the direction of flow oi the solution through said slot, a doctor blade associated with each of said rolls to wipe the surface thereof free of solution prior to leaving the same, and a guide member located intermediate and spaced from each of said rolls, said guide member extending through said slot from within said hopper toward, but not in contact with, said film forming element.

7. In a film or sheet forming device the combination with a hopper having an opening through which a film forming solution is adapted to be fed to a moving film forming element 10- cated-adjacent thereto, of means associated with said opening for directing said solution to the film forming element in the form of a sheet, said means including a pair of rollers each positioned in liquid tight contact with that portion of the hopper forming opposite sides of said opening, and spaced apart to form a slot through which the solution is adapted to flow, means for rotating each of said rollers in a direction counter to that of the fiow of solution through said slot, and means for optionally opening and closing said slot to permit or prevent, the flow of solution therethrough as desired.

8 In a film or sheet forming device the combination with a hopper having an opening through which a film forming solution is adapted to be fed to a moving film forming element lo cated adjacent thereto, of means associated with said opening for directing said solution to the film forming element in the form of a sheet, said means including a pair of rollers each positioned in liquid tight contact with that portion of the hopper forming opposite sides of said opening, and spaced apart to form a slot through which the solution is adapted to fiow, means for rotating each of said rollers in a direction counter to that of the flow of solution through said slot,

passing substantially through the center of said slot into and out of engagement with each of said apart to provide a slot therebetween in communication with the opening in the hopper through which the solution is adapted to flow, means between said hopper and rolls for rendering a liquid tight conduit between said opening and said slot, means for driving said rolls in a direction counter to the direction of flow of the solution through said slot, a doctor blade associated with each of said rolls to wipe the surface thereof free of solution prior to leaving the same,

means for optionally closing and opening said slot, and including a stopper movable along a line passing substantially through the center of said slot to and from a slot closing position wherein it extends between and engages the periphery of each of said rollers, adjusting means for moving said stopper to and from its closing position, and an elongated guide member carried by said stopper and adapted, when said stopper is moved to a slot opening position, to be located intermediate and spaced from said rollers and to extend from within said hopper toward and adjacent to said film forming element.

10. In a film or sheet forming device the combination with a hopper having an opening through which a film forming solution is adapted to be fed to a moving film forming element located adjacent thereto, of means associated with said opening for directing said solution to the film forming element in the form of a sheet, said means including a pair of rollers mounted below and adjacent said opening and spaced apart to provide a slot therebetween in communication with the opening in the hopper through which the solution is adapted to flow, means between said hopper and rolls for rendering a liquid tight conduit between said opening and said slot, means for driving said rolls in a direction counter to the direction of fiow of the solution through said slot, a doctor blade associated with each of said rolls to wipe the surface thereof free of solution prior to leaving the same, means for optionally opening and closing said slot, said means comprising a rod rotatably mounted in said hopper and extending along a vertical line passing through the center ,of said slot, a stopper adapted to extend into said slot and having arcuate surfaces conforming to the periphery of said rolls, said stopper being in threaded engagement with said rod and fixed against rotation, means for rotating said rod and fixed against rotation, means for rotating said rod to move said stopper verticallyinto and out of closing position relative to said slot, and guide member fixed to said stopper to move therewith and adapted, when said stopper is moved to a slot opening position, to be located intermediate and spaced from said rollers and to extend from. within said hopper toward and adjacent to said film forming element.

HENRY E. VAN DERHOEF. 

